1. Field of the Invention
The present invention relates to a color filter substrate and a liquid crystal display panel including the same.
2. Description of the Related Art
Liquid crystal display devices are characterized by their small size, thinness, low power consumption, and light weight, and therefore are currently in wide use for various electronic devices. In particular, active matrix-type liquid crystal display devices having switching elements are widely adopted in OA devices such as personal computers, AV devices such as television sets, mobile phones, and the like. Moreover, the recent years have seen rapid improvements in display quality, e.g., increase in the size and increase in the definition of liquid crystal display devices, improvements in the pixel effective area ratio (higher aperture ratio), wider viewing angles, or improvements in color purity.
A liquid crystal display device generally includes: a liquid crystal display panel having a pair of opposing substrates (e.g., an active matrix substrate and a color filter substrate) and a liquid crystal layer interposed between the pair of substrates; and driving circuitry for supplying predetermined signals and voltages to the liquid crystal display panel. Furthermore, a liquid crystal display device of a transmission type or transflective type includes an illuminator such as a backlight. Note that part of the driving circuitry may be formed integrally with the liquid crystal display panel. Recently, liquid crystal television sets incorporating TV receivers are also rapidly gaining prevalence.
In a liquid crystal display panel, the thickness (which may also be referred to as a cell gap) of the liquid crystal layer is defined by a component called spacers. As the spacers, particulate spacers such as plastic beads and columnar structure bodies (which may also be referred to as “columnar spacers”, “dot spacers”, or “photospacers”) which are formed on a substrate by using a photosensitive resin are employed. Although depending on the display mode, the thickness of a liquid crystal layer directly affects retardation, for example in a liquid crystal panel of the vertical alignment mode (VA mode), which is widely used in recent years. Therefore, in order to obtain a high display quality, it is important to set and maintain the thickness of the liquid crystal layer at a predetermined value. In a large-screen liquid crystal panel, it is necessary to set and maintain the thickness of the liquid crystal layer at a predetermined thickness over the entire display region, and thus optimization of the structure and location of the spacers constitutes an important technological problem.
On the other hand, as liquid crystal display panels increase in size, the “one drop filling technique” is adopted more and more frequently in the process of forming a liquid crystal layer in methods for producing a liquid crystal display panel (see, for example, Japanese Patent Publication No. 8-20627 (Patent Document 1)).
Conventionally, a method called the “(vacuum) injection technique” has widely been used. This method involves: retaining a liquid crystal cell (empty cell) within a vacuum chamber, the liquid crystal cell (empty cell) being obtained by attaching together a pair of substrates with a sealant so as to form a predetermined gap; after removing the air from within the liquid crystal cell, allowing the interior of the chamber to return to a normal atmospheric pressure while an injection inlet which is provided in a portion of a sealing section of the liquid crystal cell is in contact with a liquid crystal material; and after injecting the liquid crystal material into the liquid crystal cell by the action of atmospheric pressure, the injection inlet is sealed with resin. If such an injection technique is adopted in the manufacturing of a large-sized liquid crystal panel, injection of the liquid crystal material takes a long time, thus greatly reducing the production efficiency.
Therefore, the one drop filling technique, which can shorten the process time relative to the injection technique, is being adopted more and more.
In the one drop filling technique, as is described in Patent Document 1 above, a sealing section having a rectangular frame-like shape is formed by using a sealant on the surface of either one of a pair of substrates, and a liquid crystal material is dropped into the region surrounded by the sealing section. This is attached onto the other substrate, and the sealant is allowed to solidify (or typically “cured”), whereby a liquid crystal display panel having a liquid crystal layer is obtained. This one drop filling technique is a very important technology in the manufacturing of a large-sized liquid crystal display panel.
One of the problems of the one drop filling technique is that voids may occur in the liquid crystal layer. Various causes for voids are known. For example, Japanese Laid-Open Patent Publication No. 2002-107740 (Patent Document 2) discloses a remedy to reduce those voids which are ascribable to insufficiency in the supply of liquid crystal material. Japanese Laid-Open Patent Publication No. 11-174477 (Patent Document 3) discloses a method for reducing those voids which are ascribable to a gas which emanates from color filters and the like (including water adsorbed on the surface, e.g., color filters). Furthermore, Japanese Laid-Open Patent Publication No. 2003-84289 (Patent Document 4) discloses a remedy to reduce “low-temperature voids”, which occur at a low temperature because of the spacers not being able to conform to the changing thickness of the liquid crystal layer, which in turn is ascribable to a thermal contraction of the liquid crystal material. In a liquid crystal display panel described in Patent Document 4, two types of columnar spacers of different heights are provided, and it is ensured that, within the range of elastic deformation of the taller columnar spacers, an external load will act also on the shorter columnar spacers. As a result, the taller spacers alone will absorb shrinkage of the cell gap due to a temperature change, thus reducing the occurrence of low-temperature voids.
However, through various studies of the inventors, it has been found that voids may occur due to causes which are not even described in the above Patent Documents.
In the one drop filling technique, when attaching the other substrate after dropping a liquid crystal material into the region surrounded by a sealing section on one of the substrates, the liquid crystal material will prevail over the entire liquid crystal cell as the liquid crystal material stretches (or spreads). If the liquid crystal material is difficult to stretch (or difficult to spread), there may be local insufficiencies of liquid crystal material, thus causing voids. Since these voids do not contain any gas, they may be referred specially to as “vacuum voids”. Since vacuum voids are caused by the liquid crystal material's difficulty to stretch, they become more likely to occur as the spacer density (distribution density: the number of spacers per unit area) increases.
On the other hand, if the spacer density is too low, the distance between adjoining spacers becomes longer. Therefore, an external pressure to the liquid crystal cell, which is associated with the atmospheric pressure when opened to the atmosphere in the injection technique and in the one drop filling technique, will lead to an increased amount of deformation of the spacers and an increased amount of flexure of the glass substrates in between spacers. This leads to local narrowing of the cell gap, so that vacuum voids become more likely to occur. Moreover, the distance between adjoining spacers becomes longer with an increase in the size of the liquid crystal display panel (i.e., an increase in pixel size), thus making this problem more outstanding. Furthermore, in a frame region of the liquid crystal display panel (i.e., a peripheral region of the display region which lies inside the sealing section), there is a large distance between the particulate spacers mixed in the sealant and the spacers within the display region, so that the cell gap locally may become narrow due to flexure of the glass substrates, whereby vacuum voids may become more likely to occur.
Although problems of the one drop filling technique are illustrated above, when the injection technique is used, a decrease in throughput may occur due to the longer injection time of a liquid crystal material.